Apoptosis is a widespread process involving chromatin cleavage at 180-200 base pair intervals, nuclear condensation, cellular fragmentation and phagocytosis (Wyllie, A. H. (1980) Nature 284:555-556). It may be activated by a wide range of hormones, growth factors and cytokines (Schwartzaman, R. A. and Cidlowski, J. A. (1993) Endocrine Rev 14:133-151). Apoptosis is often the process by which HIV infected T cells are destroyed. There is growing evidence that the efficacy of certain anti-cancer agents is related to the intrinsic propensity of target cells to respond to these compounds by apoptosis (Carson, D. A. , et al. (1992) Proc. Natl. Acad. Sci. USA 89:2970-2974; Kyprianou, N. and Isaacs, J. T. (1989) Biochem. Biophys. Res. Commum. 165:73-81; and Bhalla, K., et al. (1993) Leukemia 7:563-565).
Bcl-2 is a 26 kilodalton integral membrane oncoprotein which is unique in its ability to suppress apoptosis (Tsujimoto, Y., et al. (1984) Science 226:1097-1099). Overexpression of p26 bcl-2 is responsible for follicular lymphoma and is caused by the juxtaposition of the bcl-2 gene to immunoglobulin heavy chain enhancer elements (Tsusimoto, Y., et al. (1985) Science 228:1140-1443; and Tsujimoto, Y., et al. (1984) Science 226:1097-1099) arising from a t(14;18) chromosomal translocation. The t(14;18) translocation deregulates bcl-2 expression by placing it under the control of IgG gene regulatory elements. Deregulated bcl-2 expression confers interleukin independent survival where the lifespan of precancerous B cells is extended to facilitate malignant transformation. Numerous studies have examined the consequences of bcl-2 over expression in stable transfected cell lines, transgenic mice, and antisense deletion, with the common outcome being altered cell survival. The global nature of this response is especially striking as the diversity of apoptotic stimuli which are blocked by bcl-2 including radiation, growth factor withdrawal, glucocorticoids and multiple chemotherapeutic agents (McDonnell, T. J., et al. (1989) Cell 57:79-88; Bissonnette, R. P., et al. (1992) Nature 359:552-553; Garcia, I., et al. (1992) Science 258:302-304; and Miyashita, T. and Reed, J. C. (1992) Cancer Res. 52:5407-5411).
Early studies attributed the anti-apoptosis function of bcl-2 to mitochondrial energy metabolism (Hockenberry, D., et al. (1990) Nature 348:334-336), however, the p26-bcl-2 oncoprotein has widespread subcellular localization in membranes including the nuclear envelope (Chen-Levy, Z., et al. (1989) Mol. Cell. Biol. 9:701-710; Krajewski, S., et al. (1993) Cancer Res. 53:4701-4714; Monaghan, P., et al. (1992) J. Histochem. Cytochem. 40:1819-1825; and Haldar, S., et al. (1994) Cell Death & Differentiation 1:109-115). Bcl-2 may, however, be important in maintaining membrane lipid integrity by suppressing the generation of reactive oxygen species (Hockenberry, D. M., et al. (1993) Cell 75:214-251). Some indications are that bcl-2 dimerizes with itself or a related 21 KDa protein, BAX, (bcl-2 associated protein), where bcl-2 heterodimer with BAX promotes cell survival, whence BAX/BAX homodimer predisposes to apoptosis (Oltvai, Z. N., et al. (1993) Cell 75:609-619).
It is known that glucocorticoid induced apoptosis of immature lymphocytes can be prevented by expression of bcl-2 in the lymphoid cells (Alnemri, E. S., et al. (1992) Cancer Res. 52:491-495; Allsopp, T. E., et al. (1993) Cell 73:295-307; Strasser, A., et al. (1991) Cell 67:889-899). Recently, the effects of okadaic acid (OA), a protein phosphatase inhibitor, on glucocorticoid receptor-mediated transcriptional enhancement has been described. Morphological changes typical of apoptosis were also observed in mammalian cells following treatment with this protein phosphatase inhibitor (Boe, R., et al. (1991) Exp. Cell Res. 195:237-246).
There is a need to identify compounds which modulate bcl-2's ability to alter cell survival. There is a need to identify compounds which modulate the ability of bcl-2 to prevent apoptosis. There is a need to identify compounds which can affect bcl-2 to induce apoptosis.